There most certainly is a Catholic position on harming and killing innocent people, and on destroying God’s creation on which people depend for their survival – destroying their food base, water source, and property. This commandment is not limited to harming and killing people with knives and guns, but includes ALL the various ways in which we harm people.
While the amount of greenhouse gases that a single person contributes even over a lifetime resulting in such climate change related harms is not huge – maybe only killing one person, or together with 500 others killing one person (more if concomitant harms, such as from local pollution, are included) – the fact that the person also denies this harm and strives to dissuade others from reducing their harms may be a more serious spiritual matter.
